The present invention generally relates to management of logical storage devices possessed by a storage system.
A known example of a technology relating to management of logical storage devices (LDEV) possessed by a storage system is disclosed in, for example, Japanese Patent Application Laid-open No. 2005-107645. This publication discloses a technology in which a logical unit of a second storage system present outside a first storage system is managed within the first storage system.
In addition to the need for, for example, storage systems employing a large-scale configuration having high performance and/or large capacity, there is also a need for inexpensive storage systems employing a small-scale configuration. According to a discussion by the present applicant, the use of a scale-out storage system provided with a plurality of controller modules enables a storage system to have a large-scale configuration or small-scale configuration by adjusting the number of controller modules. In this case, each controller module manages the LDEV under its control (namely, the LDEV it is able to access), but not manage LDEV under the control of other controller modules. Furthermore, a storage system may be provided with a plurality of physical storage modules having a plurality of physical storage devices, and a storage system module may be composed in the form of a set consisting of a single controller module and a single physical storage module (or in other words, the storage system may be composed of a plurality of storage system modules).
In this configuration, the following method has been proposed as a method for enabling, for example, an I/O request for accessing an LDEV under the control of a second controller module to be received by a first controller module. Namely, the first controller module manages a virtual LDEV correlated with a real LDEV managed by the second controller module. In this case, the first controller module receives an I/O request designating the virtual LDEV, and the received I/O request is transferred to the second controller module managing the real LDEV correlated to the virtual LDEV.
According to this method, the first controller module manages the virtual LDEV. Consequently, in the case of a limitation on the number of LDEV able to be managed by one controller module, the number of real LDEV able to be managed by the controller module decreases by the number of virtual LDEV being managed. In addition, since, in the first controller module, the virtual LDEV uses cache memory of the first controller module, and, in the second controller module, the real LDEV correlated to the virtual LDEV uses cache memory of the second controller module, when considering in terms of the entire storage system, data stored in the real LDEV ends up consuming the cache memory of the storage system.